Unsteady Endwall/Tip-Clearance Flows and Losses due to Turbine Rotor-Stator Interaction Free

Unsteady static pressure on the tip endwall of a 1.5-stage low-speed axial-flow turbine was measured in detail using a micro high-response pressure transducer to investigate effects of rotor-stator interaction on the endwall and tip-clearance flows which play important roles in turbine loss generation process. In the present paper, distributions of the time-averaged and the time-dependent pressures over the rust-stage rotor and the second-stage stator are presented. Also time-averaged and time-dependent random fluctuations of the pressure were analyzed to understand unsteady behaviors of the flows and the associated losses over the endwall as well as inside the blade tip clearance. These unsteady characteristics were described for three rotor speeds with different incidences or loadings. Significantly large random fluctuations occur around the blade surfaces, particularly at the inlet and the outlet of the tip gap of the leakage flows, and in a flow separated region from the blade leading edge in a large negative incidence case A strong relation was found between the random fluctuation of the endwall static pressure and the total pressure loss inside the rotor, where large random fluctuation is attributed to high loss and vice versa. It can be seen clearly that the loss generation process is fairly unsteady due to the rotor-stator interaction.